CoAP—Constrained Application Protocol—is a data communication protocol for constrained nodes and networks. One of the main goals of CoAP is to design a generic web protocol for the special requirements of this constrained environment, especially considering energy, building automation and other M2M—machine to machine-applications. The state of a resource on a CoAP server can change over time. CoAP provides an extension for observing such changes. A client registers itself with a resource by performing a GET request that includes an Observe Option. When a server receives such a request, it services the request like a GET request and, if the resulting response indicates success, establishes an observation relationship between the client and the target resource.
Patent application publication WO 2011/159985 describes a method of exchanging information between sleeping nodes over CoAP.